1. Field of the Invention
The present invention relates to an assembly apparatus for a ball screw device and an assembly method thereof used for a feed mechanism of feeding a moving body of a mechanical device such as a machine tool or a precision machine.
The present invention further relates to a parts supply device for supplying spherical parts. The present invention also relates to a parts supply method thereof.
The present invention furthermore relates to a counter device for counting the number of spheres such as steel balls at a predetermined number.
2. Description of the Background Art
A conventional assembly apparatus for a ball screw device is composed as follows. In a ball screw device, a plurality of balls are charged and circulated into a plurality of circulation passages. The circulation passages include a spiral shaft raceway groove formed on an outer circumferential face of a screw shaft and further include a nut raceway groove, which is formed on an inner circumferential face of a cylindrical nut so as to oppose to the shaft raceway groove. The circulation passages furthermore include an S-shaped connection passage formed on a top portion for connecting a nut raceway groove. To the nut of the above ball screw device, a top portion is previously fixed. Inside the nut arranged in the longitudinal direction, a ball insertion jig having ball supply holes, the number of which is the same as that of the circulation passages, is arranged at the highest position of the nut raceway groove forming the circulation passage concerned while the phase of the ball insertion jig is made to agree with the phase of the nut. Predetermined numbers of balls are aligned in each ball feed hole and continuously fed, so that the balls can be charged into the circulation passage by its own weight. Then, the balls, which have not been charged by their own weight, are pushed into the circulation passage by an insertion rod. Concerning this technique, for example, refer to Japanese Patent Examined Publication JP-B-2530401.
However, the following problems may be encountered in the conventional art described above. The predetermined numbers of balls are aligned and fed into the ball feed hole all at once and the balls, which can not be put into the ball feed hole all at once, are pushed with the insertion rod so as to charge the balls into the circulation passage. Therefore, in the case of a top type ball screw device, when the lead of the nut raceway groove is small, the balls tend to be blocked. Accordingly, the balls, which could not be charged, must be pushed into the passage with the insertion rod. As a result, there are possibilities of damaging the balls.
In the case of a ball screw device having a connection passage laid in the axial direction of the nut such as an end cap type or a deflector type ball screw device, in order to feed balls into the connecting passage of the nut arranged in the longitudinal direction, the balls must be pushed with the insertion rod. Accordingly, there is a possibility that the balls are damaged.
In addition, the following problems may be encountered. A predetermined number of balls are aligned in the ball supply hole and fed all at once. Balls, which have not been able to be put into the ball supply hole, are pushed into the hole with the insertion rod so that the balls can be charged into the circulation hole. Accordingly, the smaller the lead of the nut raceway track groove is, the more frequently the balls are blocked.
Further, since the balls are simultaneously charged into a plurality of circulation passages, it is difficult to smoothly charge the balls. Therefore, the balls, which have not been able to be put into the ball supply hole, must be pushed into the hole with the insertion rod. Accordingly, there is a possibility that the balls are damaged.
The above problems are caused in the case where the dead weight of each ball is light when a diameter of the ball to be charged into the circulation passage is small.
Furthermore, in a conventional parts supply device, spherical parts (spheres) are supplied as follows. In a bottom portion of a hopper into which the spherical parts are put, a conical inclined face and a delivery hole for delivering the spheres are provided. The spheres, which have been introduced by rotating a rotary shaft, are delivered one by one from the delivery hole into a gap formed between a conical face at a foreword end portion of a rotary rod, which is arranged being opposed to the inclined face, and the inclined face. Concerning this technique, for example, refer to Japanese Patent Unexamined Publication JP-A-6-23632.
However, the following problems may be encountered in the technique described above. A conical face of a rotary rod and an inclined face of a hopper bottom portion are arranged being opposed to each other. Into the gap, spheres are introduced by rotating the rotary rod, so that the spheres can be delivered from a delivery hole one by one. Accordingly, when the gap formed between the conical face and the inclined face is too large, an effect of rotating the rotary rod is diminished. Therefore, the spheres are collected from the periphery to the delivery hole all at once. Accordingly, the spheres are piled up and blocked.
When the gap formed between the conical face and the inclined face is too small, it is impossible to introduce the spheres into the gap. Accordingly, the spheres cannot be delivered.
Therefore, the attaching accuracy of attaching the rotary rod for forming the gap must be accurately controlled. Accordingly, in the case where a production lot of producing the spheres accommodated in the hopper is changed, it becomes necessary to highly accurately adjust the gap each time the production line is changed.
In the case where a diameter of the sphere is changed, a hole diameter of the delivery hole must be changed. Further, it is necessary to adjust a length of the rotary rod. Furthermore, it is necessary to highly accurately adjust the attaching accuracy of attaching the rotary rod. Therefore, it takes time to conduct a preparatory work of the parts supply device, which deteriorates the production efficiency.
A conventional counter for counting steel balls counts the number of the steel balls as follows. In an upper portion of a guide member formed out of a non-magnetic material in which a steel ball passage is formed, a magnet is arranged. At a lower end of this magnet, a cylindrical magnetic body and electromagnetic coil are arranged. In a lower portion of the magnetic body, a sensor is arranged and a steel ball stoppage releasing device is formed. Steel balls, which are aligned in the steel ball passage, are released when the electromagnetic coil is energized so that a magnetic force of the magnet can be canceled out and the steel ball passage can be opened, and the number of the steel balls passing through a counting sensor is counted. When a predetermined number of steel balls have passed through the counting sensor, the electromagnetic coil is energized so that a magnetic force of the magnet can be intensified, and the steel balls are stopped and the number of the steel balls is counted. Concerning this technique, for example, refer to Japanese Patent Unexamined Publication No. JP-A-6-319864.
In a periphery of a shaft body pivotally arranged in a leading passage, a spiral flange portion having a pitch larger than a diameter of a steel ball is formed. When the shaft body is rotated by a pulse motor, the number of steel balls passing, which are sent downward by the flange portion, is counted with a counting sensor. When a predetermined number of steel balls have passed through the counting sensor, the pulse motor is stopped so as to stop the steel balls, and the number of the steel balls is counted. Concerning this technique, for example, refer to Japanese Patent Unexamined Publication No. JP-A-7-617.
However, according to the technique described in JP-A-6-319864, the following problems may be encountered. In the technique described in JP-A-6-319864, the steel balls are stopped by a magnetic force. Accordingly, there is a possibility that the steel balls, which have been counted, are magnetized. Therefore, it is necessary to add a step of demagnetizing the steel balls.
Further, the steel balls are made to pass through by their dead weight. Therefore, in the case where a diameter of the steel ball is small, the dead weight becomes light. Accordingly, there is a possibility that a flow of the steel balls becomes unstable.
According to the techniques described in JP-A-6-319864 and JP-A-7-617, the number of steel balls is counted by the counting sensor. Therefore, when the counting sensor has conducted counting on a predetermined number of steel balls, it is necessary to stop a flow of the steel balls by controlling a control unit so that an electromagnetic coil and a drive unit can be operated. For the above reasons, a structure of the counter becomes complicated. Therefore, when a diameter of the steel ball to be counted is changed, it takes time to change a preparatory work of the counter.